A large percentage of the air handling systems currently in use were installed in the decades of the eighties and nineties and are of constant air volume design. These systems heated or cooled a constant and usually larger than necessary volume of air based on a designed maximum required air delivery volume. During much of the operating times of these systems, a large amount of energy is wasted in unnecessary heating or cooling of these maximum volumes of air for ventilation or the distribution of heating or cooling energy. The wasted energy translates to higher costs of manufacturing and consequently higher product costs and a less competitive position in the marketplace.
The advent of variable frequency drives created an opportunity to optimize the installed base of constant volume air handling units by converting the air handling units to variable flow. The invention matches the fan energy with energy required to move heating or cooling energy away from the heat exchangers and matches the fan energy required to provide air for ventilation. Installing a variable frequency drive to operate the air handling unit blower would allow for the heating or cooling of only the required volume of air. However, this simple retrofit solution led to other problems related to reducing the air volume through the air handling unit such as freezing of the cooling coils or overheating of the heating elements or heat exchangers. Consequently, the economic advantages of reducing the energy requirements to heat or cool a smaller volume of air were overtaken by the capital investment costs of the air handling unit mechanical and control system modifications.
The systems available now included one that held the air volume constant and varied the discharge temperature or one that held the discharge temperature constant and varied the air volume. The initial step of adding variable air volume was an improvement over the constant volume system from an energy consumption perspective but introduced other problems such as overheating heating coils or freezing cooling coils on retrofit applications. The market demanded a better solution than either of these two types of systems provided for new installations or for retrofitting a constant volume air handling system to variable air flow.
The recognition of the value in reduced operating cost of variable frequency drives in air handling units resulted in new installations incorporating variable frequency drives and their associated mechanical and control system modifications in new installations. However, the large installed base of constant volume air handing units were left without a solution offered to new installations. The recent drastic increase in energy costs has served to increase the already present market pressure for a retrofit solution of variable air flow including a variable frequency drive without the associated capital costs of replacing mechanical components and existing control systems.